ciftiTools is an R package for working with CIFTI-2 format brain imaging data. It supports the following CIFTI file types: ".dscalar.nii", ".dtseries.nii", and ".dlabel.nii". It also supports the GIFTI surface geometry file, ".surf.gii". Reading, writing, and resampling CIFTI files is made possible using the Connectome Workbench. The Workbench must be installed to use ciftiTools. Visualizing the CIFTI files is made possible using the rgl R package and integrated support of surface GIFTI files.
To get started, we load the ciftiTools package and indicate where to find the Connectome Workbench folder:
library(knitr)
library(rgl)
out_dir <- "output"
knit_hooks$set(webgl = rgl::hook_webgl)
# Sometimes the first RGL window does not render properly.
rgl.open(); rgl.close()## Registered S3 method overwritten by 'ciftiTools':
## method from
## plot.surface fields
# Replace '/path/to/workbench' with the actual path to the Connectome Workbench folder on your computer.
ciftiTools.setOption('wb_path', '../../workbench')
# Cleaner vignette document
ciftiTools.setOption("suppress_msgs", TRUE)In this vignette, we will use example data included in the ciftiTools package. The files are originally from NITRC:
cifti_fnames <- list(
dtseries = system.file("extdata", "Conte69.MyelinAndCorrThickness.32k_fs_LR.dtseries.nii", package = "ciftiTools"),
dscalar = system.file("extdata", "Conte69.MyelinAndCorrThickness.32k_fs_LR.dscalar.nii", package = "ciftiTools"),
dlabel = system.file("extdata", "Conte69.parcellations_VGD11b.32k_fs_LR.dlabel.nii", package = "ciftiTools"),
dscalar_ones = system.file("extdata", "ones.dscalar.nii", package = "ciftiTools")
)
# cifti_fnames <- list(
# dtseries = file.path("../inst/extdata", "Conte69.MyelinAndCorrThickness.32k_fs_LR.dtseries.nii"),
# dscalar = file.path("../inst/extdata", "Conte69.MyelinAndCorrThickness.32k_fs_LR.dscalar.nii"),
# dlabel = file.path("../inst/extdata", "Conte69.parcellations_VGD11b.32k_fs_LR.dlabel.nii"),
# dscalar_ones = file.path("../inst/extdata","ones.dscalar.nii")
# )
surfL_fname = system.file("extdata", "Conte69.L.inflated.32k_fs_LR.surf.gii", package = "ciftiTools")
surfR_fname = system.file("extdata", "Conte69.R.inflated.32k_fs_LR.surf.gii", package = "ciftiTools")
# surfL_fname = file.path("../inst/extdata", "Conte69.L.inflated.32k_fs_LR.surf.gii")
# surfR_fname = file.path("../inst/extdata", "Conte69.R.inflated.32k_fs_LR.surf.gii")CIFTI files organize the gray matter of the brain into “grayordinates”: vertices representing the left and right cortical surfaces, and voxels representing the subcortical gray matter structures and the cerebellum. A CIFTI file consists of two parts: (1) a NIFTI XML header which contains all the metadata including medial wall locations, subcortical structure labels, and the subcortical volumetric mask; and (2) a matrix representing all the grayordinate data. These components are read in together with read_cifti:
## Brain Structures: left cortex, right cortex
## left cortex: 30424 surface vertices, 2 measurements.
## right cortex: 30527 surface vertices, 2 measurements.
## Brain Structures: left cortex, right cortex
## left cortex: 30424 surface vertices, 2 measurements.
## right cortex: 30527 surface vertices, 2 measurements.
By default, read_cifti only reads in the left and right cortex data. The subcortical data can be included by using the argument brainstructures="all". Other brainstructure combinations can be specified too, e.g. brainstructures=c("left", "subcortical"). The full set of choices for brainstructures is any combination of "left", "right" and "subcortical", or "all" for all three.
The resulting object produced by read_cifti is a "xifti" with components data (the grayordinate data matrix, separated by brainstructure), meta (metadata, most of which is from the NIFTI XML header), and surf (surface geometry). The last component distinguishes a "xifti" from a CIFTI: the left and right cortical surface geometries are not included in CIFTI files, so they must be read from separate surface GIFTI files (ending in surf.gii). The surface must be compatible: the number of vertices must be the same, and each vertex in the CIFTI data must correspond to the vertex location in the corresponding GIFTI surface file. In this way, a "xifti" represents a combination of a CIFTI file with compatible GIFTI files for the cortical mesh.
We can add surfaces like so:
## Brain Structures: left cortex, right cortex, left geometry, right geometry
## left cortex: 30424 surface vertices, 2 measurements.
## left surface model is present.
## right cortex: 30527 surface vertices, 2 measurements.
## right surface model is present.
Alternatively, we could have provided the surfaces at the outset of reading the CIFTI file:
## Brain Structures: left cortex, right cortex, left geometry, right geometry
## left cortex: 30424 surface vertices, 2 measurements.
## left surface model is present.
## right cortex: 30527 surface vertices, 2 measurements.
## right surface model is present.
Let’s take a look! view_xifti_surface(cii) displays the cortical data on the surface mesh in an interactive Open GL window. Several default color palettes are available through the color_mode argument: "sequential" (default), "qualitative" and "diverging". The "qualitative" color mode is primarily intended for dlabel CIFTI files. The colors argument can be used to choose other palettes. The idx argument can be used to visualize different columns or time points in the data. Finaly, using the argument mode=image the Open GL window can be saved to a static image. To minimize the size of this document, we will use the image method except for one plot in the “Resampling” section.
knitr::include_graphics(view_xifti_surface(
cii, zlim=c(1,2), mode='image', fname=file.path(out_dir, "xifti_0.png")
))First time point; sequential palette
knitr::include_graphics(view_xifti_surface(
cii, idx=2, zlim=c(1,5), color_mode='diverging', mode='image',
fname=file.path(out_dir, "xifti_1.png")
))Second time point; diverging palette
cii <- read_cifti(cifti_fnames$dlabel, surfL=surfL_fname, surfR=surfR_fname)
knitr::include_graphics(view_xifti_surface(
cii, mode='image', fname=file.path(out_dir, "xifti_2.png")
)).dlabel file; first label; qualitative palette
view_xifti_volume(cii) displays the subcortical data in slices. To view interactively in a web browser, set use_papaya=TRUE. By default, a series of slices is displayed overlaid on the MNI template. The orientation, numbers of slices, index and value range can be adjusted.
# cifti_fnames$dscalar_ones is the only file with subcortical data
cii <- read_cifti(cifti_fnames$dscalar_ones, brainstructures="subcortical")
view_xifti_volume(cii)## Values to be plotted range from 1 to 1.
Subcortical data (all ones)
# For information only, since papaya viewer cannot be opened during knitting
view_xifti_volume(cii, num.slices=10, use_papaya = TRUE)The "xifti" “plot” method (plot(cii)) will display the cortical data if possible, and the subcortical data otherwise.
"xifti"Medial wall vertices are not included in the cortex_left and cortex_right components of data. A data matrix for the left cortex which includes the medial wall vertices can be obtained with unmask_cortex(cii$data$cortex_left, cii$meta$cortex$medial_wall_mask$left) (and similarly for the right cortex).
Sometimes, the medial wall locations are not indicated in the XML header of the CIFTI file. In this case, ciftiTools attempts to infer medial wall locations from 0 or NA values in the cortical data when read_cifti() is called.
The subcortical data is stored in vectorized form. To recover the subcortical volume, use unmask_vol(cii$data$subcort, cii$meta$subcort$mask, fill=NA) for the data and unmask_vol(cii$meta$subcort$labels, cii$meta$subcort$mask, fill=0) for the labels.
cii$meta$cifti$intent indicates the NIFTI intent, which corresponds to a unique CIFTI file type. For example, "dtseries.nii" files have an intent of 3006.
A "surface" can be read in using make_surf(surfL_fname). They can be viewed with view_surf or, equivalently, their plot method.
knitr::include_graphics(plot(
make_surf(surfR_fname), hemisphere="right", mode="image",
fname=file.path(out_dir, "surf_1.png")
))Right hemisphere surface
A "xifti" can contain surface geometry without the corresponding data; to make it, use as.xifti(surfL=make_surf(surfL_fname)).
"xifti" and writing itWe can make a "xifti" from data using as.xifti. For example, let’s make a "xifti" from the mean image (over time) of the "dtseries.nii" file. (Note that the dtseries used in this example does not truly contain fMRI timeseries data, but we use it for illustration.)
cii <- read_cifti(cifti_fnames$dtseries)
cii_new <- as.xifti(
cortexL = apply(cii$data$cortex_left, 1, mean),
cortexL_mwall = cii$meta$cortex$medial_wall_mask$left,
cortexR = apply(cii$data$cortex_right, 1, mean),
cortexR_mwall = cii$meta$cortex$medial_wall_mask$right
)
is.xifti(cii_new)## [1] TRUE
We can also include artifical subcortical data using the mask from "ones.dscalar.nii".
cii2 <- read_cifti(cifti_fnames$dscalar_ones, brainstructures="subcortical")
vol <- cii2$data$subcort
vol <- vol - 1 + matrix(rnorm(nrow(vol)*ncol(vol)), nrow=nrow(vol))
cii_new <- as.xifti(
cortexL = apply(cii$data$cortex_left, 1, mean),
cortexL_mwall = cii$meta$cortex$medial_wall_mask$left,
cortexR = apply(cii$data$cortex_right, 1, mean),
cortexR_mwall = cii$meta$cortex$medial_wall_mask$right,
subcortVol = cii2$data$subcort,
subcortLabs = cii2$meta$subcort$labels,
subcortMask = cii2$meta$subcort$mask
)
is.xifti(cii_new)## [1] TRUE
## Brain Structures: left cortex, right cortex, subcortex
## left cortex: 30424 surface vertices, 1 measurements.
## right cortex: 30527 surface vertices, 1 measurements.
## subcortical: 31870 voxels, 1 measurements.
## subcortical labels:
##
## Cortex-L Cortex-R Accumbens-L Accumbens-R Amygdala-L
## 0 0 135 140 315
## Amygdala-R Brain Stem Caudate-L Caudate-R Cerebellum-L
## 332 3472 728 755 8709
## Cerebellum-R Diencephalon-L Diencephalon-R Hippocampus-L Hippocampus-R
## 9144 706 712 764 795
## Pallidum-L Pallidum-R Putamen-L Putamen-R Thalamus-L
## 297 260 1060 1010 1288
## Thalamus-R
## 1248
To visualize the cortical data of the new xifti object, we need to add the surface geometry:
cii_new <- add_surf(cii_new, surfL=surfL_fname, surfR=surfR_fname)
knitr::include_graphics(view_xifti_surface(
cii_new, mode="image", fname=file.path(out_dir, "xifti_3.png"),
title=".dtseries Mean Image", zlim=c(0,4)
)).dtseries mean image
Here’s the subcortical data:
## Values to be plotted range from 1 to 1.
Subcortical data (with random noise)
We can also write out a new CIFTI file with write_cifti! Here’s how:
written_cii_fname <- file.path(out_dir, "my_new_cifti.dscalar.nii")
write_cifti(cii_new, written_cii_fname)## Writing left cortex.
## Writing right cortex.
## Writing subcortical data and labels.
## Creating CIFTI file from separated components.
# Verify that if we read the file back in, the result matches.
# Some metadata is lost or added, but beside that, the data is the same.
cii_new_copy <- read_cifti(written_cii_fname, brainstructures="all")
try(testthat::expect_equal(cii_new$data, cii_new_copy$data))## Error : cii_new$data not equal to cii_new_copy$data.
## Component "cortex_left": Mean relative difference: 3.584765e-08
## Component "cortex_right": Mean relative difference: 3.548024e-08
There is only a negligible difference between the original and the written-then-read copy due to rounding.
ciftiTools can resample CIFTI files to a lower resolution. Here, we resample the 32k "dtseries.nii" file to 6k vertices. We also provide the surfaces and resample them in conjunction.
resampled_cii_fname <- "my_new_resampled.dtseries.nii"
resampled_surfL_fname <- "my_resampled_surfL.surf.gii"
resampled_surfR_fname <- "my_resampled_surfR.surf.gii"
cii_6k <- resample_cifti(
cifti_fnames$dtseries, resampled_cii_fname,
resamp_res = 6000,
surfL_fname, surfR_fname,
resampled_surfL_fname, resampled_surfR_fname,
write_dir=out_dir
)## Separating CIFTI file.
## Time difference of 1.961601 secs
## Resampling CIFTI file.
## Time difference of 6.818666 secs
## Merging components into a CIFTI file...
## Time difference of 0.1714261 secs
The new files can be viewed together with read_cifti. Let’s make this one interactive, since the meshes are now much lower-res! Try clicking and dragging around the plot to rotate, and scrolling to zoom in and out. We’ll also use a blue background color to highlight this interactive figure within the vignette.
view_xifti_surface(
read_cifti(cifti_fname=cii_6k["cifti"], surfL=cii_6k["surfL"], surfR=cii_6k["surfR"]),
zoom=7/10, bg="#d4edf5", cex.title=1.25,
title=".dtseries resampled to 6k", zlim=c(0,2)
)
# Note: Call rglwidget() here to display inline in RStudio.
# rglwidget() does not work with htmlpreview, so we used the WebGL hook instead.